To date, a variety of systems have been introduced which utilize a combination of a heat pump cycle and a secondary battery that charges and discharges for system electric power. However, it is known that, in general, charge-discharge characteristics of the secondary battery are greatly influenced by temperature of the secondary battery itself. Thus, a system has been disclosed which utilizes heat generated by a heat pump in order to adjust the temperature of the secondary battery to an appropriate temperature (Patent Literature 1, for example).
Moreover, in a system having a secondary battery and a heat pump equipped with a water storage tank, a configuration has been disclosed in which the secondary battery is heated by supplying the battery with heat of hot water of intermediate temperatures in the storage tank when the temperature of the secondary battery is lower than a predetermined temperature (Patent Literature 2, for example).
In Patent Literature 1, the heat comes from the heat pump is used to heat the secondary battery. The configuration described above improves charge-discharge efficiency of the secondary battery; however, efficiency of the heat pump is adversely reduced.
Moreover, even with the configuration disclosed in Patent Literature 2, the efficiency of the secondary battery is improved at the cost of the efficiency of the heat pump.